1. Field of the Invention
The present invention relates to a silicon acceleration sensor and the fabricating method thereof, and particularly to a bridge-type silicon acceleration sensor having eight beams and the fabricating method thereof.
2. Description of the Prior Art
A silicon sensor, which senses acceleration, vibration or the like, is basically classified into two types based on the mechanical structure mounting a mass thereon: a cantilever-type and a bridge-type. Currently, a bridge-type acceleration sensor having two or four beams, that is, a bridge-type acceleration sensor supporting the mass thereof by two or four beams, is well known to a person in the art. However, a bridge-type acceleration sensor supporting the mass thereof at eight directions (hereinafter, called as an 8-beam bridge-type acceleration sensor) has been not introduced up to now because of the difficulty in precisely shaping the microstructure when a silicon substrate is etched by a conventional isotropic etching process.
Furthermore, the 8-beam bridge-type acceleration sensor has been not taken into consideration till now because the sensitivity thereof is nothing but 25% as compared with a two-beam bridge-type acceleration sensor.
On the other hand, a S/N ratio (signal to noise ratio) is the most important thing in the art of the silicon acceleration sensor, which is determined by directional selectivity. Because the conventional cantilever-type or bridge-type acceleration sensor has poor directional selectivity, additional stoppers for preventing the mass portion from being vibrated or accelerated toward undesirable directions, for example, the left and/or right directions, should be provided in the vicinity of the mass portion.
As a result, a precise and complicated process is required due to the provision of the stoppers, and there occurs another problem such as shock noise and abrasion between the mass portion and the stoppers.
To solve the problems of the conventional acceleration sensor, the inventer has devised an 8-beam bridge-type acceleration sensor using a microstructure fabrication method incorporating a porous silicon which has been being lively studied in recent.